a. Field of the Invention
The present invention relates to a liquid developer for use in electrophotography which is prepared by uniformly dispersing a toner consisting essentially of pigment or dyestuff and non-aqueous resinous composition in a carrier liquid having a high insulating property and a low dielectric constant.
B. Description of the Prior Art
Conventional liquid developers for use in electrophotography are generally prepared by dispersing a toner consisting essentially of pigment such as carbon black or dyestuff and synthetic or natural resin such as acrylic resin, phenol-modified alkyd resin, steberite resin, polymerized rosin and synthetic rubber, admixed with a polarity-controlling agent such as lecithin, metallic soap, linseed oil and higher fatty acid, in a carrier liquid having a high insulating porperty and a low dielectric constant such as a petroleum-type aliphatic hydrocarbon. In the early stages following their manufacture, the resin in the toner adheres to the pigment or dyestuff and the toner not only maintains a distinct positive or negative polarity but also retains uniform dispersion stability. Such a toner undergoes electrophoresis according to the electric charge of the electrostatic latent image formed on the sensitive surface of a photosensitive material in the development process and is fixed thereon to form a copied image, but it is defective in that the resin and the polarity-controlling agent therein gradually diffuse in the carrier liquid with the passing of time, so that the polarity becomes indistinct and finally there occurs coagulation, resulting in a lowering of the fixing efficiency and the formation of an opaque or indistinct copied image. Moreover, the conventional toner is incapable of re-dispersion once it coagulates, and accordingly reuse thereof has not been feasible.